The present invention is,directed to a valve system for an internal combustion engine. More particularly, the present invention is directed to a valve system that can be modified during engine operation to improve engine performance.
An internal combustion engine typically includes a series of valves that may be actuated to control the intake and exhaust of gases that flow to and from the combustion chambers of the engine. A typical engine will include at least one intake valve and at least one exhaust valve for each combustion chamber in the engine. The opening of each of the valves is timed to occur at a certain point in the operating cycle of the engine. For example, an intake valve is typically opened when a piston is withdrawing in its cylinder to allow fresh air to enter the combustion chamber. An exhaust valve is typically opened after combustion and when the piston is advancing within the cylinder to expel the exhaust gas from the combustion chamber.
The actuation, or opening and closing, of the engine valves may be controlled in a number of ways. For example, each engine valve may be driven by a cam that is operatively connected to the engine crankshaft. The rotation of the engine crankshaft causes a corresponding rotation of each cam, which, in turn, actuates the corresponding engine valve. Because the rotation of the crankshaft also controls the motion of the piston, this type of arrangement may be used to coordinate the actuation of each engine valve with the desired portion of the engine operating cycle.
Recent research into engine operation has revealed that modifying the timing of the valve actuation based on the operating conditions of the engine may improve the efficiency of the engine and/or reduce the emissions generated by the engine. For example, an engine may be operated on a Miller cycle to reduce the emissions generated by the engine. In a Miller cycle, the actuation of the intake valves is modified so that the intake valves either remain closed for a portion of the intake stroke or remain open for a portion of the compression stroke. This has been found to reduce the generation of emissions. However, the benefits of the Miller cycle are typically achieved when the engine is operating under steady loads. An engine that operates solely on the Miller cycle may be difficult to start.
Accordingly, to take full advantage of the Miller cycle, and other such valve actuation modifications, an engine requires a valve timing system that may be modified to adjust the valve timing based on the operating conditions of the engine. One example of an engine that includes a variable valve timing system is described in U.S. Pat. No. 5,682,854. In this engine, a cam driven valve system is supplemented with an additional cam that may be rotated by an actuator that is independent of the engine crankshaft. Rotation of the additional cam will change the phase of the cams that actuate one intake valve and one exhaust valve. Changing the phase of the cams will modify the timing of the valve actuation. Thus, this system may be used to modify the timing of the valve actuation during engine operation.
However, adding the additional cam to the valve system increases the complexity of the valve system. The increased complexity may result in an increased cost of the engine. In addition, the additional parts may require more maintenance and may be more susceptible to failure. Accordingly, such an engine may experience undesirable down time due to maintenance and/or repair of the valve system.
The valve system of the present invention solves one or more of the problems set forth above.
One aspect of the present invention is directed to a valve system for an engine. A cylinder head defines an intake passageway, an exhaust passageway, and an auxiliary passageway. The auxiliary passageway includes a first connection with the intake passageway and a second connection with the exhaust passageway. A control valve is disposed in the auxiliary passageway. The control valve is moveable between a first position where the control valve blocks the first connection between the auxiliary passageway and the intake passageway and a second position where the control valve blocks the second connection between the auxiliary passageway and the exhaust passageway.
In another aspect, the present invention is directed to an engine that includes an engine block defining at least one combustion chamber. A cylinder head is configured to engage the engine block. The cylinder head defines an intake passageway that leads to the combustion chamber, at least one exhaust passageway that leads from the combustion chamber, and an auxiliary passageway that leads from the combustion chamber. An auxiliary valve element is disposed in the auxiliary passageway for movement between an open position and a closed position. A piston is disposed in the combustion chamber for movement between a bottom dead center position and a top dead center position. The piston has a combustion bowl configured to receive the auxiliary valve element when the piston is at the top dead center position and the auxiliary valve element is in the open position.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.